Conventional read out circuits for computer disc drives must detect low level analog input signals which may vary by orders of magnitude and settle those signals as quickly as possible to within a nominal range for submission to analog to digital converters (ADC) and subsequent digital processing. Because a finite time is required to settle the signal, each data field on the disc is formatted with a tracking zone or preamble field ahead of the data field to provide sufficient time for the signal to be brought within the nominal range. Since the preamble field occupies space on the disc that could be used to store data, faster settling is desirable to increase usable disc capacity. One attempt to improve performance uses two digital loops, an acquisition loop and a tracking loop. These loops sense deviations in the signal and feed back a correction signal to a variable gain adjustment amplifier to compensate for variations in the input signal. The acquisition loop adjusts for large input signal variations such as occur initially when a read command is received. The tracking loop adjusts for small signal variations as occur during operation. Such digital dual loop systems offer satisfactory performance but have certain shortcomings. The acquisition loop is relatively long and so its response time is not as short as would be desirable. Further, since the acquisition loop is digital the sampling of the analog input signal by the ADC must be carefully timed to insure that variations in amplitude that would require gain adjustment are true amplitude variations in the input signal and not merely phase or sampling shifts. This requires substantial additional complex circuitry.